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Results: 1 through 26 of 26 (4.777 secs)
You searched for: creator:"Markus Boettcher"
[texts]Modeling the Emission Processes in Blazars - Markus Boettcher
Blazars are the most violent steady/recurrent sources of high-energy gamma-ray emission in the known Universe. They are prominent emitters of electromagnetic radiation throughout the entire electromagnetic spectrum. The observable radiation most likely originates in a relativistic jet oriented at a small angle with respect to the line of sight. This review starts out with a general overview of the phenomenology of blazars, including results from a recent multiwavelength observing campaign on 3C2...
Downloads: 1
[texts]Modeling the Spectral Energy Distributions and Variability of Blazars - Markus Boettcher
In this review, recent progress in theoretical models for the broadband (radio through gamma-ray) emission from blazars are summarized. The salient features of both leptonic and hadronic models are reviewed. I present sample modeling results of spectral energy distributions (SEDs) of different types of Fermi-detected blazars along the traditional blazar sequence, using both types of models. In many cases, the SEDs of high-frequency peaked blazars (HBLs) have been found to be well represented by ...
[texts]Constraints on the Geometry of the VHE Emission in LS 5039 from Photon-Photon Deabsorption - Markus Boettcher
A detailed parameter study of the gamma-gamma absorption effects in LS 5039 is presented. For a range of plausible locations of the VHE gamma-ray emission region and the allowable range of viewing angles, the de-absorbed, intrinsic VHE gamma-ray spectra and total VHE photon fluxes and luminosities are calculated and compared to luminosity constraints based on wind accretion onto the compact object in LS 5039...
Downloads: 59
[texts]Models for the Spectral Energy Distributions and Variability of Blazars - Markus Boettcher
In this review, recent progress in theoretical models for blazar emission will be summarized. The salient features of both leptonic and lepto-hadronic approaches to modeling blazar spectral energy distributions will be reviewed. I will present sample modeling results of spectral energy distributions (SEDs) of different types of blazars along the blazar sequence, including Fermi high-energy gamma-ray data, using both types of models...
Downloads: 8
[texts]Synchrotron Emission from VHE Gamma-Ray Induced Pair Cascades in AGN Environments - Parisa Roustazadeh
The discovery of very-high-energy (VHE, E > 100 GeV) gamma-ray emission from intermediate- and low-frequency peaked blazars suggests that gamma-gamma absorption and pair cascading might occur in those objects. In previous papers, we investigated the Compton emission from VHE gamma-ray induced pair cascades, deflected by moderate magnetic fields, in a largely model-independent way, and demonstrated that this emission can explain the Fermi fluxes and spectra of the radio galaxies Cen A and NGC 127...
Downloads: 2
[texts]X-ray Spectral Signatures of the Photon Bubble Model for Ultraluminous X-ray Sources - Justin Finke
The nature of ultraluminous X-ray sources in nearby galaxies is one of the major open questions in modern X-ray astrophysics. One possible explanation for these objects is an inhomogeneous, radiation dominated accretion disk around a $\sim 10 M_{\odot}$ black hole -- the so-called ``photon bubble'' model. While previous studies of this model have focused primarily on its radiation-hydrodynamics aspects, in this paper, we provide an analysis of its X-ray spectral (continuum and possible edge and ...
Downloads: 1
[texts]VHE Gamma-Ray Induced Pair Cascades in the Radiation Fields of Dust Tori of AGN: Application to Cen A - Parisa Roustazadeh
The growing number of extragalactic high-energy (HE, E > 100 MeV) and very-high-energy (VHE, E > 100 GeV) gamma-ray sources that do not belong to the blazar class suggests that VHE gamma-ray production may be a common property of most radio-loud Active Galactic Nuclei (AGN). In a previous paper, we have investigated the signatures of Compton-supported pair cascades initiated by VHE gamma-ray absorption in monochromatic radiation fields, dominated by Ly-alpha line emission from the Broad Line Reg...
Downloads: 1
[texts]Time-dependent Radiation Transfer in the Internal Shock Model Scenario for Blazar Jets - Manasvita Joshi
We describe the time-dependent radiation transfer in blazar jets, within the internal shock model. We assume that the central engine, which consists of a black hole and an accretion disk, spews out relativistic shells of plasma with different velocity, mass, and energy. We consider a single inelastic collision between a faster (inner) and a slower (outer) moving shell. We study the dynamics of the collision and evaluate the subsequent emission of radiation via the synchrotron and synchrotron sel...
Downloads: 1
[texts]A Time Dependent Leptonic Model for Microquasar Jets: Application to LSI 61 303 - Swati Gupta
The Galactic high-mass X-ray binary and jet source (microquasar) LSI +61 303 has recently been detected at TeV gamma-ray energies by the MAGIC telescope. We have applied a time-dependent leptonic jet model to the broadband spectral energy distribution and suggested (though not unambiguously detected) orbital modulation of the very high energy gamma-ray emission of this source. Our model takes into account time dependent electron injection and acceleration, and the adiabatic and radiative cooling...
Downloads: 2
[texts]Synchrotron Emission from Pair Cascades in AGN Environments - Parisa Roustazadeh
Recent detections of very-high-energy (VHE, E > 100 GeV) gamma-ray blazars which do not belong to the high frequency peaked BL Lac (HBL) class, suggest that gamma-gamma absorption and pair cascading might occur in those objects. In the presence of even weak magnetic fields, these Compton-supported pair cascades will be deflected and contribute to the Fermi gamma-ray flux of radio galaxies. We demonstrate that, in this scenario, the magnetic field can not be determined from a fit of the cascade e...
Downloads: 5
[texts]An Angle Dependent SSC Model for Relativistic Jet Sources - Omar Jamil
We report on the development of a numerical code to calculate the angle-dependent synchrotron + synchrotron self-Compton radiation from relativistic jet sources with partially ordered magnetic fields and anisotropic particle distributions. Using a multi-zone radiation transfer approach, we can simulate magnetic-field configurations ranging from perfectly ordered (unidirectional) to randomly oriented (tangled)...
Downloads: 1
[texts]Synchrotron and Synchrotron Self-Compton Spectral Signatures and Blazar Emission Models - James Chiang
We find that energy losses due to synchrotron self-Compton (SSC) emission in blazar jets can produce distinctive signatures in the time-averaged synchrotron and SSC spectra of these objects. For a fairly broad range of particle injection distributions, SSC-loss dominated synchrotron emission exhibits a spectral dependence $F_\nu \sim \nu^{-3/2}$. The presence or absence of this dependence in the optical and ultraviolet spectra of flat spectrum radio quasars such as 3C~279 and in the soft X-ray s...
Downloads: 3
[texts]Flash-Heating of Circumstellar Clouds by Gamma Ray Bursts - Charles D. Dermer
The blast-wave model for gamma-ray bursts (GRBs) has been called into question by observations of spectra from GRBs that are harder than can be produced through optically thin synchrotron emission. If GRBs originate from the collapse of massive stars, then circumstellar clouds near burst sources will be illuminated by intense gamma radiation, and the electrons in these clouds will be rapidly scattered to energies as large as several hundred keV...
Downloads: 10
[texts]VHE Gamma-Ray Induced Pair Cascades in Blazars and Radio Galaxies: Application to NGC 1275 - Parisa Roustazadeh Sh.
Recent blazar detections by HESS, MAGIC, and VERITAS suggest that very-high-energy (VHE, E > 100 GeV) gamma-rays may be produced in most, if not all, types of blazars, including those that possess intense circumnuclear radiation fields. In this paper, we investigate the interaction of nuclear VHE gamma-rays with the circumnuclear radiation fields through gamma-gamma absorption and pair production, and the subsequent Compton-supported pair cascades...
Downloads: 10
[texts]Timing Signatures of the Internal-Shock Model for Blazars - Markus Boettcher
We investigate the spectral and timing signatures of the internal-shock model for blazars. For this purpose, we develop a semi-analytical model for the time-dependent radiative output from internal shocks arising from colliding relativistic shells in a blazar jet. The emission through synchrotron and synchrotron-self Compton (SSC) radiation as well as Comptonization of an isotropic external radiation field are taken into account...
Downloads: 3
[texts]Implications of the VHE Gamma-Ray Detection of the Quasar 3C279 - Markus Boettcher
The MAGIC collaboration recently reported the detection of the quasar 3C279 at > 100 GeV gamma-ray energies. Here we present simultaneous optical (BVRI) and X-ray (RXTE PCA) data from the day of the VHE detection and discuss the implications of the snap-shot spectral energy distribution for jet models of blazars. A one-zone synchrotron-self-Compton origin of the entire SED, including the VHE gamma-ray emission can be ruled out...
Downloads: 2
[texts]Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects - Justin Finke
We introduce a methodology for analysis of multiwavelength data from X-ray selected BL Lac (XBL) objects detected in the TeV regime. By assuming that the radio--through--X-ray flux from XBLs is nonthermal synchrotron radiation emitted by isotropically-distributed electrons in the randomly oriented magnetic field of a relativistic blazar jet, we obtain the electron spectrum. This spectrum is then used to deduce the synchrotron self-Compton (SSC) spectrum as a function of the Doppler factor, magne...
Downloads: 1
[texts]Time-Dependent Synchrotron and Compton Spectra from Jets of Microquasars - Swati Gupta
Jet models for the high-energy emission of Galactic X-ray binary sources have regained significant interest with detailed spectral and timing studies of the X-ray emission from microquasars, the recent detection by the HESS collaboration of very-high-energy gamma-rays from the microquasar LS~5039, and the earlier suggestion of jet models for ultraluminous X-ray sources observed in many nearby galaxies...
Downloads: 3
[texts]Nonthermal Synchrotron and Synchrotron Self-Compton Emission from GRBs: Predictions for {\em Swift} and {\em GLAST} - Justin Finke
Results of a leptonic jet model for the prompt emission and early afterglows of GRBs are presented. The synchrotron component is modeled with the canonical Band spectrum and the synchrotron self-Compton component is calculated from the implied synchrotron-emitting electron spectrum in a relativistic plasma blob. In the comoving frame the magnetic field is assumed to be tangled and the electron and photon distributions are assumed to be isotropic...
Downloads: 2
[texts]The External Shock Model of Gamma-Ray Bursts: Three Predictions and a Paradox Resolved - Charles D. Dermer
In the external shock model, gamma-ray burst (GRB) emissions are produced by the energization and deceleration of a thin relativistic blast wave due to its interactions with the circumburst medium (CBM). We study the physical properties of an analytic function which describes temporally-evolving GRB spectra in the limit of a smooth CBM with density n(x)\propto x^(-\eta), where x is the radial coordinate...
Downloads: 13
[texts]The Hard VHE Gamma-ray Emission in High-Redshift TeV Blazars: Comptonization of Cosmic Microwave Background Radiation in an Extended Jet? - Markus Boettcher
Observations of very-high-energy (VHE, E > 250 GeV) gamma-ray emission from several blazars at z > 0.1 have placed stringent constraints on the elusive spectrum and intensity of the intergalactic infrared background radiation (IIBR). Correcting their observed VHE spectrum for gamma-gamma absorption even by the lowest plausible level of the IIBR provided evidence for a very hard (photon spectral index Gamma_{ph} 4 X 10^6) on kiloparsec scales along the jet.
Downloads: 2
[texts]Time dependent simulations of multiwavelength variability of the blazar Mrk 421 with a Monte Carlo multi-zone code - Xuhui Chen
(abridged) We present a new time-dependent multi-zone radiative transfer code and its application to study the SSC emission of Mrk 421. The code couples Fokker-Planck and Monte Carlo methods, in a 2D geometry. For the first time all the light travel time effects (LCTE) are fully considered, along with a proper treatment of Compton cooling, which depends on them. We study a set of simple scenarios where the variability is produced by injection of relativistic electrons as a `shock front' crosses ...
Downloads: 8
[texts]Gamma-Ray Studies of Blazars: Synchro-Compton Analysis of Flat Spectrum Radio Quasars - Charles D. Dermer
We extend a method for modeling synchrotron and synchrotron self-Compton radiations in blazar jets to include external Compton processes. The basic model assumption is that the blazar radio through soft X-ray flux is nonthermal synchrotron radiation emitted by isotropically-distributed electrons in the randomly directed magnetic field of outflowing relativistic blazar jet plasma. Thus the electron distribution is given by the synchrotron spectrum, depending only on the Doppler factor $\delta_{\r...
Downloads: 2
[texts]Time-dependent simulations of emission from FSRQ PKS1510-089: multiwavelength variability of external Compton and SSC models - Xuhui Chen
[abridged] We present results of modeling the SED and multiwavelength variability of the bright FSRQ PKS1510-089 with our time-dependent multizone Monte Carlo/Fokker-Planck code (Chen et al. 2001). As primary source of seed photons for inverse Compton scattering, we consider radiation from the broad line region (BLR), from the molecular torus, and the local synchrotron radiation (SSC). Different scenarios are assessed by comparing simulated light curves and SEDs with one of the best flares by PK...
Downloads: 2
[texts]Simultaneous B'V'R' Monitoring of BL Lacertae Object S5~0716+714 and Detection of Inter-Band Time Delay - Jianghua Wu
We present the results of our optical monitoring of the BL Lac object S5 0716+714 on seven nights in 2006 December. The monitoring was carried out simultaneously at three optical wavelengths with a novel photometric system. The object did not show large-amplitude internight variations during this period. Intranight variations were observed on four nights and probably on one more. Strong bluer-when-brighter chromatism was detected on both intranight and internight timescales...
Downloads: 2
[texts]Multiwavelength Spectral Studies Of Fermi-LAT Blazars - Manasvita Joshi
We present multiwavelength spectral analyses of two Fermi-LAT blazars, OJ 287 and 3C 279, that are part of the Boston University multiwaveband polarization program. The data have been compiled from observations with Fermi, RXTE, the VLBA, and various ground-based optical and radio telescopes. We simulate the dynamic spectral energy distributions (SEDs) within the framework of a multi-slice, time-dependent leptonic jet model for blazars, with radiation feedback, in the internal shock scenario...
Downloads: 3
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